A 33-year-old American man who grew up in Minnesota and then moved to California was killed over the weekend in Syria while battling alongside the militant grew formerly known as ISIS, NBC News reported on Tuesday.

According to the network, Douglas McAuthur McCain was killed
over the weekend while fighting with the Islamic State, or IS,
against members of a separate opposition group in Syria. Family
members confirmed his passing to NBC, and senior administration
officials speaking anonymously acknowledged that they were aware
of the man’s death.

US officials have not spoken further on the record about the
incident, but NBC’s Cassandra Vinograd and Ammar Cheikh Omar
wrote on Monday that activists with the Free Syrian Army
confirmed the news and provided the network with photographs of
McCain’s body containing tattoos that correlate with images on
his public Facebook profile and Twitter account.
Additionally, NBC reported that the activists also located
McCain’s travel documents.

“The battle in itself seemed tragically normal. Two Syrian
opposition groups fought and there were heavy casualties on both
sides,” the journalists wrote. “Then victorious rebels
rifled through the pockets of the dead. One contained about $800
in cash -- and an American passport.”

“He was a normal guy who was social, open-minded, liked to
smile always, and always wanted to be a good Muslim,” one
acquaintance of the man told NBC. “He was a goofball in high
school,” added another former classmate.

To one senior administration official, though, Americans who
travel abroad to fight among the ranks of groups like the Islamic
State pose a very real problem to security back in the States.

"The threat we are most concerned about to the homeland is
that of fighters like this returning to the US and committing
acts of terrorism," NBC quoted the unnamed official as
saying.

The US Department of State has previously spoken out to condemn
the activities of any Americans who may have traveled abroad, and
last week a spokesperson for the agency said that thousands of
fighters from outside of Syria have since traveled to the
war-torn nation to take up arms in its three-year-old civil war.

“We think that there are approximately 12,000 fighters from
at least 50 countries in Syria -- foreign fighters, including a
small number of Americans -- that may have traveled to Syria
since the beginning of the conflict" deputy State Department
spokeswoman Marie Harf said on Thursday. "They may all not still be
there," she added.

Indeed, at least one American — a Florida man named Moner
Mohammad Abusalha — has previously died in Syria after carrying
out a suicide bombing mission this past May.

"The Abusalha case is an object lesson in how difficult it is
to identify self-radicalized people in the US, and to track
people who go from the US to Syria and return,” one senior
law enforcement official told NBC at the time. “This difficulty has been a
repeated subject of publicly expressed concern for months."

“Syria is attracting more foreign fighters than Afghanistan did
in its heyday,” Thomas Joscelyn, a senior fellow at the
Foundation for Defense of Democracies, previously told Business Insider.